The invention relates to passive thermal control enclosures for controlling the temperature of the contents of the enclosure, and in particular aspects relates to such enclosures for payloads transported into earth orbit.
There are a number of situations in which thermal control of materials and objects of various types is required for substantial periods of time. Payloads, especially scientific experiments, transported and stored on-orbit on the Space Shuttle and International Space Station (ISS), are subjected to a series of severe environmental conditions (vibration, shock, temperature variations, pressure variations, etc.). For human space-flight, there are a number of constraints and requirements that limit the materials, configuration, etc., associated with cargo. Cost, power availability, limitations on available space, and the need for minimum crew time and effort, are also factors that must be considered.
Providing a controlled temperature for various payloads, especially experiments, in a secure, light-weight container is a critical need.
There are a number of refrigerator/freezer designs that have been developed and used on the Shuttle Orbiter, Spacelab, and Spacehab, and additional units that are being readied for the ISS. However, the power, mass, thermal control (waste heat removal) and special access provisions associated with these designs can be highly limiting to their application. For example, for the Orbiter, there are periods when power and waste heat removal are not available for the refrigerator/freezers (e.g., periods of several hours before, and during, ascent and descent). There are also limitations on where these refrigerator/freezers can be located on the ISS. For example, only powered ISPRs can be used for these units.
There are situations in which materials and objects must be transported on Earth under constant, controlled temperature conditions with little or no access to power and waste heat removal. These instances include transport of biological specimens, including tissue and blood, pharmaceuticals, etc. The types of refrigerator/freezers or insulation containers used for terrestrial applications are completely unsuitable for space applications, due to their design limitations.
Payload transport also is limited by the Space Shuttle and ISS facilities, which are severely limited and heavily subscribed. Mass constraints are also an important issue, and due to the high inclination orbit of the ISS, much of the carrier capacity for the Shuttle racks and lockers cannot be fully utilized, which further constrains the use of refrigerator/freezers requiring special attachments, power, waste heat removal, and health monitoring instrumentation.
The only known passive containers that can be used for transporting and stowing substantial amounts of materials and/or payloads are unpowered lockers and soft stowage bags used for transporting various articles that do not require temperature control. There are no known passive control containers with substantial cargo volumes (of the order of a Mid-deck Locker Equivalent) for the ISS and Shuttle. Existing passive temperature-control containers are limited to small dewars, used to transport or store small quantities of material.
The refrigerator/freezers for the Space Shuttle and ISS have substantial usable volume, but they require power, and thus must be placed in special powered racks with waste heat removal capabilities. These, and other factors, limit the use of such active refrigerator/freezers.
The present invention addresses the above needs and achieves other advantages by providing a passive, low-cost, safe, and secure controlled-temperature carrier suitable especially for transporting payloads to orbit and conducting long-term experiments requiring stowage for total mission periods of hundreds of hours. Minimal effort is required of the astronauts or ground crew to service and maintain the unit. The unit is capable of holding essentially the same, or greater, volumes and masses as other powered refrigerator/freezers in the NASA inventory, and it can achieve constant temperatures over a wide temperature range (xe2x88x9220 C. to +40 C.), through choice of an appropriate phase change material (PCM).
A passive thermal control enclosure in accordance with one preferred embodiment of the invention comprises:
an inner enclosure having a plurality of walls joined together to form a generally box-shaped configuration, the inner enclosure having an opening at one end thereof, the walls of the inner enclosure comprising a rigid structural material and at least some of the walls also including a thermally insulating material;
an outer enclosure having a plurality of walls joined together to form a generally box-shaped configuration surrounding the inner enclosure such that there is a space between each wall of the inner enclosure and a corresponding wall of the outer enclosure, the outer enclosure having an opening at one end thereof in registration with the opening in the inner enclosure for inserting items into and removing items from the inner enclosure;
an inner door releasably engaged with the inner enclosure for closing the opening therein, and an outer door releasably engaged with the outer enclosure for closing the opening therein;
a thermally insulating body disposed in the space between each wall of the inner enclosure and the corresponding wall of the outer enclosure, each thermally insulating body comprising a plurality of insulators stacked together to provide redundancy such that if one insulator loses its insulating ability there is at least one other insulator for insulating the corresponding wall of the inner enclosure; and
at least one sealed pack of phase change material disposed inside the inner enclosure.
Preferably, the insulators between the inner and outer enclosures each comprises a vacuum-sealed flexible package filled with an insulating material. The insulating material in the insulators preferably comprises an aerogel, and more preferably is a carbon and silica aerogel.
In a preferred embodiment, the walls of the inner enclosure comprise fiber-matrix composite material. More particularly, preferably the top, bottom, and side walls of the inner enclosure each comprises a sandwich structure having fiber-matrix composite skins between which a core of thermally insulating material is disposed. The core of thermally insulating material preferably comprises a honeycomb material.
The inner enclosure preferably includes a latch assembly for latching the inner door closed. The preferred latch assembly comprises a pair of sliding latches that slide in opposite directions from each other for latching the inner door.
The outer enclosure preferably includes a pressure equalization vent allowing gases to pass into and out from the space between the inner and outer enclosures. The vent prevents liquids from passing therethrough.
A preferred pack of phase change material comprises a quantity of phase change material contained within a sealed first package, and a sealed second package that contains the first package. Various phase change materials can be selected depending on the required temperature at which the payload is to be maintained, and other factors. Deuterium oxide, water, various paraffins, and TEA-16 are suitable choices.
In accordance with another aspect of the invention, a passive thermal control enclosure comprises:
an inner enclosure;
an outer enclosure surrounding the inner enclosure such that a space exists between the inner enclosure and the outer enclosure; and
insulators disposed between the inner and outer enclosures, the insulators each comprising an aerogel material contained within a vacuum-sealed flexible package.
In accordance with still another aspect of the invention, a passive thermal control enclosure for use in microgravity comprises:
an inner enclosure of generally box-shaped configuration having an opening at one end thereof;
an outer enclosure of generally box-shaped configuration having an opening at one end thereof, the inner enclosure being disposed inside the outer enclosure such that the openings of the two enclosures are in registration with each other;
thermal insulators disposed between the inner and outer enclosures;
an inner door releasably engageable with the inner enclosure for closing the opening thereof, and an outer door releasably engageable with the outer enclosure for closing the opening thereof; and
latches for at least one of the inner and outer doors, the latches being configured such that the latches are movable between latched and unlatched positions by application of force pairs exerted in opposite directions such that substantially no net reaction force is exerted on the person applying the force pairs.
A passive thermal control enclosure in accordance with yet another aspect of the invention comprises:
an inner enclosure;
an outer enclosure surrounding the inner enclosure such that a space exists between the inner enclosure and the outer enclosure;
insulators disposed between the inner and outer enclosures; and
sealed packs of phase change material disposed within the inner enclosure for surrounding a payload to be temperature-controlled, the phase change material comprising deuterium oxide.
The invention also encompasses a method for transporting a temperature-sensitive payload between earth and a spacecraft in orbit about earth and for storing the payload on the spacecraft. The method comprises:
placing the payload in a passive thermal control enclosure containing sealed packs of phase change material having a phase transition temperature generally corresponding to a temperature at which the payload is to be maintained;
transporting the passive thermal control enclosure containing the packs of phase change material and the payload to the spacecraft and transferring the passive thermal control enclosure to a storage area in the spacecraft; and
when a substantial fraction of the phase change material has changed phase, removing the packs of phase change material from the passive thermal control enclosure and inserting fresh packs of the phase change material into the enclosure.
Preferably, the packs of phase change material are initially placed into the thermal control enclosure in a frozen state and are removed when a substantial fraction of the phase change material has melted, and the melted packs of phase change material are refrozen onboard the spacecraft. The step of re-freezing the packs of phase change material preferably comprises cooling each pack such that the phase change material freezes along a freeze front that travels in substantially only one direction. The phase change material preferably is packaged in flexible packages to accommodate expansion of the phase change material during re-freezing.